1. Field of the Invention
The present invention relates to a polymerization initiator having a novel structure and conjugated diene polymers prepared using the polymerization initiator.
2. Description of the Related Art
Generally, the single use of a rubber as a tire material is insufficient to achieve desired physical properties of the tire. For the purpose of enhancing the physical properties (e.g., tread wear and frictional force) of a tire, it is common practice to add various reinforcing materials in the manufacture of the tire. A mixture of carbon black as an organic reinforcing material and silica as an inorganic reinforcing material is currently used in the manufacture of tires.
Nevertheless, several problems have been encountered in the use of the reinforcing materials. One of the problems is poor compatibility between the reinforcing materials and tire rubbers. This poor compatibility may make the reinforcing materials immiscible with the rubbers, leading to deterioration in the physical properties of the finished tire. On the contrary, good compatibility between reinforcing materials and rubbers in the manufacture of tires can ensure improved tread wear, reduced rolling resistance and improved wet traction of the tires.
Under such circumstances, various methods have been proposed to improve the compatibility of reinforcing materials, particularly, carbon black and silica with conjugated diene polymers. Of these, a representative method is to substitute the ends of a polymer with functional groups that have a high affinity for reinforcing materials. For example, one end of a polymer is modified with an amine compound to improve the compatibility with carbon black as an organic reinforcing material and the other end thereof is modified with a compound having another functional group to improve the compatibility with silica as an inorganic reinforcing material.
Methods for introducing functional groups into polymers can be largely divided into two methods: the first method is to modify one end of a polymer with different compounds and the second method is to use an initiator having one or more functional groups to introduce the functional groups into a polymer.
According to the second method, active ends of the polymer other than the initiator moiety can be modified with another functional compound, and as a result, both ends of the polymer can be modified. In comparison with the substitution of one end of the polymer, the modification of both ends of the polymer is advantageous in that the compatibility between the polymer and one or more reinforcing materials can be maximized.
Prior art techniques for modifying both ends of a polymer with a monofunctional initiator containing at least one amine moiety can be found in the literature, for example, see EP 0,476,640, EP 0,626,278 and U.S. Pat. No. 5,523,371.
Prior art techniques for modifying both ends of a polymer with a bifunctional initiator can be found in the literature, for example, see U.S. Pat. Nos. 4,182,818 and 4,196,153.
Prior art techniques regarding organolithium polymerization initiators can be found in the literature, for example, see U.S. Pat. Nos. 4,067,917, 4,161,494, 4,172,190 and 3,954,894.
There are large differences between the prior art techniques disclosed in the references and the present invention relating to novel organolithium compounds and compounds including the organolithium compounds.
As described above, there is a need to develop novel polymers that are highly miscible with inorganic reinforcing materials in the manufacture of tires. Thus, the inventors of the present invention have endeavored to develop a rubber that is compatible with carbon black as well as silica, and as a result, have found that a rubber produced by modifying the ends of a novel bifunctional initiator containing amine moieties with a silane compound showed greatly improved tread wear and dynamic physical properties, compared to other rubber products using only silica as a reinforcing material. The present invention has been accomplished based on this finding.